In recent years, there have been many developments in the field of cardiac assistance, with a plethora of devices and systems for aiding the pumping of a dysfunctional heart. One common approach is to use a pacemaker that provides an electrical pulse that causes the heart to dilate. Another approach is to perform a heart transplant, replacing the heart with a donor heart. A further approach is to use an artificial heart. Artificial hearts are particularly useful as short term, bridging solutions until appropriate donor hearts are available.
A third approach is to provide a heart assist device, essentially a prosthetic that is wrapped around the heart, or a part thereof, such as to the left ventricle, for example. Contraction of the prosthetic provides a squeezing force on the heart helping it to pump.
A variety of mechanical cardiac devices have been developed, including pumps that serve as ventricular assist devices and full artificial hearts. Each device performs differently and is appropriate for a different specific function.
In 1969, the world's first total artificial heart implant was performed by Dr. Denton A. Cooley. The device, developed by Dr. Domingo Liotta, was implanted in a 47-year-old patient with severe heart failure, and supported the patient for nearly three days, until a donor heart was found allowing transplantation. The Liotta total artificial heart was an air-driven (pneumatic), double-ventricle pump. Wada-Cutter hingeless valves controlled the flow of blood through the inflow and outflow areas of the pump. The two pump chambers (the “ventricles”), the cuff-shaped inflow tracts (the “atria”), and the outflow tracts were lined with a special fabric that promoted the formation of a smooth cellular surface. The flexible inflow and outflow tracts were made of Dacron fabric, and the pump chambers were made of Dacron fabric and Silastic plastic. The pumps were connected to the external power unit with Silastic tubing covered by Dacron fabric. The console, also a major engineering accomplishment at the time, was about the size of a large household washing machine. Two pneumatic power units generated the pumping and vacuum actions needed to move blood through the artificial heart. The complex control panel included numerous switches and knobs used to adjust pumping rate and pumping pressure.
In July 1981, Dr. Cooley again implanted a total artificial heart. Developed by Dr. Tetsuzo Akutsu at the Texas Heart Institute, the Akutsu III total artificial heart was implanted in a 36-year-old man, keeping him alive for 55 hours, until a donor heart was found for transplantation. The Akutsu III total artificial heart contained two air-powered, double-chambered pumps. The pumping chambers were made of a smooth material called Avcothane, which could be molded in one piece. The inflow and outflow ports contained Bjork-Shiley disc valves. The prosthetic ventricles were attached to the remnants of the natural heart's atria and to the great vessels by flexible inflow and outflow conduits with detachable quick-connectors. The pumps were connected with Dacron velour-covered tubing to an external control console. The control console had three basic systems: a pneumatic (air-driven) drive system, an electrical monitoring/control system, and an electrical power system. The pneumatic drive system provided both pressure and vacuum to each ventricle. Under normal use, the console was connected to wall pressure and vacuum sources. During patient transport, or in the event of in-house power failure, the system automatically switched to on-board compressed air tanks. Monitoring of heart rate and systolic duration were the primary functions of the electrical monitoring/control system. The monitoring/control system provided a digital readout of driveline pressure and vacuum supplied, as well as the status of standard and emergency power supplies. The electrical power system had two independent sources of power: standard AC/DC power and a back-up battery in case of power failure.
The Jarvik-7 total artificial heart, designed by Dr. Robert Jarvik is probably the best known of the artificial heart devices. It is designed to function like the natural heart. It was first implanted in a patient named Barney Clark in 1982, who survived for 112 days. By the late 1980s, surgeons had used the Jarvik-7 as a bridge to transplantation in more than 70 patients. Subsequently, the Jarvik-7 was called the Symbion total artificial heart. Today, it is known as the CardioWest total artificial heart and is still in use as a bridge to transplantation.
The Jarvik-7 has two pumps, much like the heart's ventricles. Each sphere-shaped polyurethane “ventricle” has a disk-shaped mechanism that pushes the blood from the inlet valve to the outlet valve. The ventricles are pneumatically (air) powered. Air is pulsed through the ventricular air chambers at rates of 40 to 120 beats per minute. The artificial heart is attached to the heart's natural atria by cuffs made of Dacron felt. The drivelines out of the ventricular air chambers are made of reinforced polyurethane tubing. Where they exit the skin, the lines are covered with velour-covered Silastic which ensures stability and encourages tissue growth even with movement by the patient. The air-driven, external power system powers the pump through drivelines that enter the heart through the patient's left side. The large console on wheels is as large and as heavy as a household refrigerator. It is normally connected to sources of compressed air, vacuum, and electricity. The system is backed up by a rechargeable battery in case of power failure and includes on-board compressed air tanks (modified scuba type) for use during patient transport. Controls in the console allow the doctor to control pump rate, pumping pressure, and other essential functions.
The AbioCor™ implantable replacement heart represents the culmination of 30 years of research, development, and testing conducted by ABIOMED, Inc. and its collaborators, with the support of the National Heart, Lung and Blood Institute. It was the first completely self-contained total artificial heart and is designed to sustain the body's circulatory system and to extend the lives of patients who would otherwise die of heart failure. Unlike other systems described hereinabove, it is totally implanted within the body, and patients are not tethered to a large, air-pumping console nor do they have wires or tubes piercing their skin. The AbioCor is intended for use in end-stage heart failure patients whose hearts have irreversible left and right ventricular failure and for whom surgery or medical therapy is inadequate.
The AbioCor consists of a thoracic unit, an internal rechargeable battery, an electronics package and external console. The thoracic unit (the pump) weighs around a kilogram and consists of the artificial ventricles, which contain their corresponding valves, and a motor-driven hydraulic pumping system. The hydraulic pumping system uses pressure to shuttle blood from side to side, from the artificial right ventricle to the lungs or from the artificial left ventricle to the rest of the body. To create this pressure, the pump's motor rotates at 4000 to 8000 revolutions per minute. The internal rechargeable battery is an emergency battery that is continually charged by the external power source. The internal battery can provide up to 20 minutes of operation while disconnected from the main battery pack. The electronics package is implanted in the patient's abdominal area and monitors and controls the pumping speed of the artificial heart. The AbioCor is normally powered by an external console or battery packs. The internal battery powers the pump only when the external power supply is disconnected. Power to the AbioCor is achieved with an energy-transfer device called a transcutaneous energy transmission (TET) system. The TET system consists of internal and external coils that are used to transmit power across the skin. Because tubes or wires do not pierce the skin, the chances of developing an infection are decreased. External battery packs can power the AbioCor for 4 hours.
The ABIOMED BVS-5000 is currently in use worldwide for temporary left, right, or biventricular (both ventricles) support in patients with potentially reversible heart failure. The BVS-5000 underwent preclinical studies at the Texas Heart Institute (THI) from 1986 to 1988 and was introduced for use in patients at THI in 1988. It was the first heart assist device approved by the U.S. Food and Drug Administration for the support of post-cardiotomy patients (those who have developed heart failure as a result of heart surgery). Since that time, hundreds of patients have been sustained by the BVS-5000. In addition to post-cardiotomy support, the BVS-5000 may also be used for donor heart dysfunction or donor heart failure after heart transplantation, right-sided heart failure after placement of a left ventricular assist device, after acute heart attack or acute heart disorders, such as viral myocarditis, after trauma to the heart, after disease of the heart muscle (cardiomyopathy).
In patients whose hearts have not recovered after temporary support, the BVS-5000 may be used as a bridge to another device or as a bridge to heart transplantation. The air-driven blood pump is placed outside the body (extra corporeally). A unique feature of the BVS-5000 system is its dual-chamber design, which is similar to the natural heart, and provides support for either the left or right ventricle, or both. The pump houses two polyurethane chambers: an atrial chamber that fills with blood through gravitational force and a ventricular chamber that pumps blood by air-driven power. The atrial chamber is vented outside the patient. The ventricular chamber is connected to the power console by a 0.25-inch pneumatic (air) line. Two trileaflet valves separate the atrial and ventricular chambers. The pump can produce blood flow of up to 5 liters per minute. Cannulas of various designs (for blood drainage and return) are available to accommodate different patient anatomy. The BVS-5000 console can support one or two blood pumps. It is fully automatic and compensates for changes both in preload and after load. The left and right sides are triggered independently of each other. A backup battery provides 1 hour of support, and an alarm sounds when only 10 minutes of power remain. A foot pump can also serve as a backup power source. By using the console to limit blood flow; patients can be slowly weaned from support.
A related device, the Abiomed AB5000 Circulatory Support System is a short-term mechanical circulatory support system that can provide left, right, or biventricular support for patients whose hearts have failed but have the potential for recovery. The AB5000 can be used to support the heart, giving it time to rest—and potentially recover native heart function. The device can also be used as a bridge to definitive therapy.
Since January 1986, when Dr. O. H. Frazier of the Texas Heart Institute initiated clinical trials thereof, the Thoratec HeartMate®IP LVAS is in use worldwide as a bridge to heart transplantation. It provides physical rehabilitation and greatly improves the clinical status of bridge-to-transplant patients. When patients are supported by the HeartMate for more than 30 days, the outcome of transplantation improves. The pneumatic (air-driven) LVAS pump is a titanium alloy pump that weighs 570 grams and consists of a blood chamber, an air chamber, a driveline, and inflow and outflow conduits. Each conduit is a titanium cage that contains a 25-mm porcine (pig) valve within a woven Dacron-fabric graft. A flexible polyurethane diaphragm separates the blood chamber and the air chamber. Textured surfaces within the blood chamber promote the development of a cellular lining, which helps prevent blood clots and infection. With a stroke volume of 83 milliliters and a maximum pumping rate of 140 beats per minute, the IP LVAS can provide flow rates of up to 12 liters per minute. The HeartMate console powers and controls the implanted IP LVAS blood pump. A 6-foot cable joins the blood pump to the drive console. Another 6-foot long tubing connects from the pump to the console to push air into the pump chamber. A front panel display gives a continuous readout of the pump rate, stroke volume, and total blood flow. The system can operate in three modes: automatic mode, fixed-rate mode, and external (synchronous) mode. The drive console is easy to operate and can be transported on a wheeled cart, allowing patients to move about the hospital.
The Thoratec Heartmate® XVE LVAS was developed and tested by Thermo Cardiosystems, Inc. and the Texas Heart Institute. In 1991, the system was implanted in a patient who was subsequently supported for 505 days and was able to leave the hospital while being supported by this device, paving the way for other patients to routinely wait at home for their transplants. Because the system is relatively easy to use, patients and their families can maintain it outside the hospital setting. Patients can live at home, return to work, and resume a more normal lifestyle while awaiting a suitable donor heart. Recently, the (FDA) approved the HeartMate XVE LVAS as permanent support for end-stage heart failure patients not eligible for heart transplants. The titanium blood pump thereof consists of a blood chamber, a motor chamber, a driveline, and inflow and outflow conduits. The pump weighs a mere 1150 grams. Each conduit contains a 25-mm porcine (pig) valve within a woven Dacron-fabric graft. A polyurethane diaphragm separates the blood chamber and the motor chamber. Textured surfaces within the blood chamber promote the development of a cellular lining, which help prevent blood clots and infection. The XVE LVAS has a maximum stroke volume of 83 milliliters and can be operated at up to 120 beats per minute, resulting in flow rates of up to 10 liters per minute.
The XVE LVAS's external equipment includes a system controller, a power base unit, and a 20-foot power cable, as well as batteries and other accessories. The system controller continuously monitors and controls the implanted motor and shows information regarding alarm conditions. The power base unit serves as a battery charger and as an interface between the system monitor and the implanted pump. The 20-foot power cable allows the system to be operated by AC power. Alternatively, patients can wear a portable battery pack around their waist, which permits the system to be operated tether-free for up to 8 hours.
A further development of the XVE LVAS, the Thoratec HeartMate® II LVAS was developed and tested by Thoratec Corporation, Inc., and the Texas Heart Institute (THI). The HeartMate II is being evaluated initially for use as a bridge to transplantation. Eventually, it is hoped that the HeartMate II can be used for destination therapy—as permanent support for end-stage heart failure patients who are not eligible for heart transplantation.
The HeartMate II is a high-speed, axial flow, rotary blood pump. As an axial flow device, the HeartMate II produces no pulsatile action. Weighing 12 ounces (about 375 grams) and measuring about 1.5 inches (4 cm) in diameter and 2.5 inches (6 cm) long, it is significantly smaller than other currently approved devices. As such, it may be suitable for a wider range of patients, including small adults and children. The internal pump surfaces are fabricated from smooth, polished titanium. Within the pump is a rotor that contains a magnet. The rotor assembly is rotated by the electromotive force generated by the motor. The rotor propels the blood from the inflow cannula out to the natural circulation. The pump speed can vary from 6,000 rpm to 15,000 rpm, providing blood flow of up to 10 liters per minute. The pump can run in two operating modes: fixed speed and auto-speed. In fixed-speed mode, the device operates at a constant speed, which can be adjusted via the system monitor. In the auto-speed mode, the pump speed varies in response to different levels of patient or cardiac activity. The HM II LVAS's external equipment includes a system driver, a power base unit, and a 20-foot power cable, as well as batteries and other accessories. The system driver continuously monitors and controls the implanted motor and shows information regarding alarm conditions. The power base unit serves as a battery charger and an interface between the system monitor and the implanted pump. The 20-foot power cable allows the system to be operated by AC power. Patients can wear a portable battery pack around their waist, which permits the system to be operated tether-free for three hours.
The Thoratec Ventricular Assist Device (VAD) can be used to support patients with acute and chronic heart failure. Doctors have gained approximately 20 years of experience with this system at numerous medical centers around the world. One or two Thoratec VADs can be used to provide left, right, or biventricular support. The blood pump is positioned extra corporeally and is connected to tubes (cannulas) inserted into the heart. The pump has a rigid plastic case that contains a flexible pumping sac. Blood is ejected from the pump when the pumping sac is compressed by air from the external control console. Within the inflow and outflow conduits, mechanical valves control the direction of blood flow. The Thoratec VAD has a stroke volume of 65 milliliters. It can be operated at up to 100 beats per minute, resulting in blood flow rates of up to 7 liters per minute.
The Thoratec console has control modules and internal compressors that provide pressure and vacuum conditions to the pump. The drive console delivers air to the blood pump in a pulse-like fashion, causing blood to be ejected into the aorta and/or pulmonary artery. The drive console may be set to three different modes of operation: (i) an asynchronous mode where pumping occurs at a preset rate, (ii) a synchronous mode where pumping is synchronized with the patient's heart rate and (iii) a volume mode where pumping is adjusted according to the left ventricular filling volume. The console continuously displays the ejection pressure, percent ejection time, pump rate, pump flow, and vacuum pressure. Because of the external placement of the pump(s), patient mobility is limited with this system.
Jarvik Heart, Inc. and the Texas Heart Institute began developing the Jarvik 2000 FlowMaker® in 1988. About the size of a “C” battery, the device is a valve-less, electrically powered axial flow pump that fits directly into the left ventricle and continuously pushes oxygen-rich blood throughout the body. To date, patients have been sustained for more than 400 days with this device. The Jarvik 2000 FlowMaker is an axial flow blood pump that uses electrical power to rotate a vaned impeller—the only moving part. The device is 2.5 cm wide, 5.5 cm long, and weighs 85 grams. The impeller is a neodymium-iron-boron magnet, which is housed inside a welded titanium shell. The impeller is supported by ceramic bearings. A small cable, which exits the body through the abdominal walls delivers power to the impeller. All of the blood-contacting surfaces are made of highly polished titanium. The normal operating range for the control system is 8,000 to 12,000 revolutions per minute, which will generate an average pump flow rate of 5 liters per minute. The pump speed is controlled by an analog system controller. The pump speed can be manually adjusted from 8000 to 12000 rpm in increments of 1000. The control unit monitors the pump function and the remaining power in the batteries. Audible and visual alerts notify the user of any problems.
The Levitronix CentriMag Short-term LVAS comprises a single-use centrifugal pump, a motor, and a primary drive console. Compared to other devices, the Levitronix LVAS is unique in that it is designed to operate without mechanical bearings or seals. This is possible because the motor magnetically levitates the impeller, achieving rotation with no friction or wear.
In the United States, the Levitronix CentriMag LVAS is still under investigation for use as a short-term device that would provide circulatory support of up to 14 days for patients with post-cardiotomy cardiogenic shock, i.e. those who have developed heart failure as a result of heart surgery.
The Levitronix CentriMag is an extra-corporeal, continuous-flow, centrifugal-type rotary blood pump. The pump housing and rotor are made of medical-grade polycarbonate, designed for single-use. The only moving component within the pump is the impeller, which is magnetically levitated and rotated in a contact-free manner. The centrifugal pump design permits rotation of the impeller at lower speeds, while still achieving desired flow rates. The pump can rotate at speeds of 1500 rpm to 5500 rpm and can provide flow rates of up to 9.9 liters per minute.
The Levitronix pump causes very little damage to the blood because it does not contain any bearings or seals—components that are known to cause hemolysis and promote thrombus formation. In addition, the pump does not contain any flexing sacs, diaphragms, or valves, minimizing the risk of component failure and device-related adverse effects.
The TandemHeart Percutaneous Ventricular Assist Device (pVAD) differs from other assist devices in that it can be inserted either by cardiovascular surgeons in the operating room or by cardiologists in the cardiac catheterization laboratory. The TandemHeart has been used in post-cardiotomy cardiogenic shock patients, and as a bridge to a definitive therapy. The TandemHeart pVAD provides short-term support from a few hours up to 14 days, giving the heart time to strengthen and potentially regain native function.
The TandemHeart pVAD is an extra-corporeal, continuous-flow centrifugal assist device. Cannulas are inserted percutaneously through the femoral vein and advanced across the intra-atrial septum into the left atrium. The pump withdraws oxygenated blood from the left atrium, propels it by a magnetically driven, six-bladed impeller through the outflow port, and returns it to one or both femoral arteries via arterial cannulas. The pump weighs 8 ounces and is capable of delivering blood flow up to 3.5 liters per minute. The pump also has a proprietary fluid-infusion system that provides cooling and lubrication to the impeller and enhances thromboresistance. The system provides localized anticoagulation to the blood inside the pump, reducing the need for systemic anticoagulation.
The TandemHeart pVAD is operated by a controller console designed to continuously monitor the system. The console also has extensive back-up and fault-management features.
The Bio-Pump was originally developed for cardiopulmonary bypass, but it can be used for up to about a week of circulatory support beyond the surgical setting. The Bio-Pump has been used both in post-cardiotomy cardiogenic shock patients and as a bridge to transplantation for patients who cannot be weaned from the device. This short-term assist device can be implanted in a broad range of patients, from newborns to adults, and can be used alone or along with another Bio-Pump or other type of assist device if biventricular support is needed.
The Bio-Pump is an extra-corporeal, centrifugal device that can provide support for one or both ventricles. Two disposable models are available: the 80-mL model for adults and a 48-mL model for children. The transparent pump housing is shaped like a cone. The pump consists of an acrylic pump head with inlet and outlet ports placed at right angles to each other. The impeller, which is a stack of parallel cones, is driven by an external motor and power console. Rotation of this impeller at high speeds creates a vortex, which drives blood flow in relation to rotational speed. Blood enters through an inlet at the top of the cone and exits via an outlet at the base. The adult model pump can rotate up to 5000 rpm and can provide flow rates of up to 10 liters per minute.
The Bio-Pump console is relatively small and easy to operate, although it does require continuous supervision by specially trained personnel. When fully charged, the system has an internal battery life of 45 minutes. A battery indicator light displays the charge level. A flow probe inserted in the patient's artery allows for a continuous readout of the blood flow rate. The operator can program the console for use in children or adults by selecting a high or low flow rate. The console features a numeric readout and a bar graph that shows flow rate and revolutions per minute.
The Model-7 ALVAD is a pneumatic abdominal left ventricular assist device (ALVAD) that has been used to support post-cardiotomy patients.
The Model-7 ALVAD is a pneumatic, single-chambered implantable blood pump that was placed in the abdomen and connected to the left ventricle by a Dacron tube. Blood from the left ventricle flows through the tube and fills a polyurethane bladder. When air from the driveline fills the space between the bladder and the titanium pump housing, the blood is pumped through a disc-type valve into the aorta and to the body. Polyester fibers coat all of the blood-contacting surfaces, except the valve discs and the inflow and outflow grafts. The fibers promote the development of a cellular lining, which helps prevent blood clots and infection. The console thereof provides variable settings of pump chamber pressurization, pump chamber filling, and pulse duration. The two modes of operation include EKG-triggered pumping that is synchronized with the resting and pumping phases of the left ventricle, or variable fixed-rate asynchronous pumping. Four fail-safe functions are also available in cases of EKG interruption; mechanical or electrical failure; loss of external pneumatic power or loss of AC line power. The internal power supplies allow for portable operation for up to 50 minutes.
The Impella Recover LD/LP 5.0 Support System has been developed to address the need for ventricular support in patients who develop cardiogenic shock—heart failure after heart surgery—and who have not responded to standard medical therapy. The system is designed to provide immediate support and restore hemodynamic stability for a period of up to 7 days. Used as a bridge to therapy, it allows time for developing a definitive treatment strategy.
The Impella Recover system is a miniaturized impeller pump located within a catheter. The device can provide support for the left side of the heart using either the Recover LD 5.0 that is implanted via direct placement into the left ventricle, or the Recover LP 5.0 LV that is placed percutaneously through the groin and positioned in the left ventricle. The microaxial pump of the Recover LP/LD 5.0 can pump up to 4.5 L/min at a speed of 33,000 rpm. The pump is located at the distal end of a 9 Fr catheter. At its largest outside diameter, which contains the pump housing, the Impella measures 21 Fr. The catheter shaft contains the electrical connections for the pump motor and sensor as well as for a separate tube used for transfer of purged fluid.
Clinical use of the Hemopump in patients began at the Texas Heart Institute in April 1988 as a short-term treatment for cardiogenic shock. Later, the device was evaluated as an alternative to standard cardiopulmonary bypass. Today, the Hemopump is no longer used, but researchers have applied its design to other circulatory assist devices. The innovative design of the Hemopump included a tiny axial flow pump that provided up to 3.5 liters per minute of circulatory support. The first patient treated with the Hemopump was a 61-year-old man with profound heart failure related to donor heart rejection. His life was sustained with the Hemopump for two days, and he was eventually discharged from the hospital. The catheter-mounted, intra-aortic axial flow pump thereof is about the size of the eraser on an ordinary pencil. It was inserted through a small incision in the femoral or external iliac artery, advanced to the aorta, and positioned across the aortic valve. A screw element rotated 17,000 to 25,000 times per minute, drawing blood from the left ventricle and ejecting it into the descending aorta. Power was provided through a percutaneous driveline connected to an external electromechanical console. The console produced flows of up to 3.5 liters per minute and assumed up to 80% of the left ventricle's workload.
Dr. Adrian Kantrowitz introduced the intra-aortic balloon pump (IABP) in the late 1960s as a simple yet effective device to increase coronary perfusion. Because it is easy to insert, the IABP is the most widely used form of mechanical circulatory support. At the Texas Heart Institute, the IABP is now used in more than 450 patients each year. Although the IABP was first used for surgical patients, the pump can now be used along with interventional cardiology procedures and medications. Indications for its use include failure to wean from cardiopulmonary bypass, cardiogenic shock, heart failure, acute heart attack, support during high-risk percutaneous transluminal coronary (balloon) angioplasty, rotoblator procedures, and coronary stent placement.
The IABP is a polyethylene balloon mounted on a catheter, which is generally inserted into the aorta through the femoral artery in the leg. The pump is available in a wide range of sizes (2.5 cc to 50 cc) that will fit patients of any age and size. The balloon is guided into the descending aorta, approximately 2 cm from the left subclavian artery. At the start of diastole, the balloon inflates, augmenting coronary perfusion. At the beginning of systole, the balloon deflates; blood is ejected from the left ventricle, increasing the cardiac output by as much as 40 percent and decreasing the left ventricular stroke work and myocardial oxygen requirements. In this manner, the balloon supports the heart indirectly. The balloon is inflated with helium, an inert gas that is easily absorbed into the bloodstream in case of rupture. Inflation of the balloon can be triggered according to the patient's electrocardiogram, their blood pressure, a pacemaker (if they have one), or by a pre-set internal rate.
The IABP is driven by the balloon pump console. The operating controls are located on a touch pad below the display monitor and can be programmed to produce rates as high as 140 beats per minute. The on-board battery provides power for up to 2 hours. The New CS100 IntelliSync console, with one-button start up, automatically adapts to patients' changing conditions.
Similarly, U.S. Pat. No. 6,406,422 to Landesberg describes a ventricular assist method and apparatus having an expandable intraventricular chamber, essentially a single chambered balloon, for dilating a heart chamber. The device described is not intended to replace the entire function of a failing heart but rather to add additional cardiac input.
PCT/IL2004/000500 (WO 2005/002645) to Ben Shalom et al. describes a hydraulic system and method for supporting a body organ, the system comprising a closed loop liquid-tight tubing fitted with a pressure generator for propelling a liquid through the system, an organ engaging member connected to a pressure chamber via a discharge valve for controlled discharge of liquid into the organ inflatable pressure member. The organ-engaging member includes an inflatable pressure member suited for receiving the organ. There is further provided at least one control valve for selectively controlling liquid flow through the system and a controller for selectively controlling the discharge valve and the at least one control valve. The system may be used as cardiac assist device or for massaging a limb to stimulate blood flow therethrough. The device described has one pulsation chamber, and there is an inherent lack of flexibility therewith in that the system described includes no features for adapting the prosthetic ring to specific diseased hearts.
U.S. Pat. No. 4,192,293 to Asrican, describes a cardiac assist device that operates by cyclically exerting pressure through an implanted inflatable sheath, which surrounds the myocardium. The sheath is rigid and encloses a bladder or plurality of bladders into which a fluid, either in the form of an inert gas or a liquid is pulsed, with a time displacement curve similar or identical to the contraction-distension characteristics exhibited normally by the myocardium during a cardiac cycle. Pulsing is triggered by the EKG R-spike of the patient, which operates a valve. In order to provide adequate fluid volume for the required pressure through the valve, an elastic fluid reservoir is provided. The cyclical pressure is generated by an elastic wall. It is therefore a fixed pressure that is difficult to match to a specific heart, and in practice will only provide a very approximate match. Furthermore, since clearly the appropriate cardiac assistance for an individual varies considerably throughout the day, between sleeping and walking for example, and depends, inter alia, on the amount of exertion and the quality of the air breathed, such a system will only very approximately match actual requirements.
WO 98/55165 to Seare and Woodard, describes a cardiac assist device with independently operable pneumatic or hydraulic chambers. In consequence thereof, the pressure provided at different positions on heart may be varied. The overall shape of the device described may be cup shaped, frustoconical, cylindrical etc. and may be tailored to the shape of the individual heart to provide a tailored solution for a specific diseased heart.
U.S. Pat. No. 5,713,954 to Rosenberg et al. describes a cuff that may be inflated and deflated using hydraulic fluid, which is designed to be placed around the natural heart. The cuff comprises a plurality of tubular segments that are variably fluid filled. Hydraulic pumps and rotating valves are described. Actuators and electronic control are also discussed.
U.S. Pat. No. 6,206,820 to Kazi describes an external prosthetic ring having elastic, fluid-fillable chambers supported by mechanical abutments, essentially inelastic plates, for cardiac assist purposes. The device described includes a plurality of fluid fillable chambers, and can be engineered to apply local pressure on part of the heart only, such as to the left ventricle, for example.
U.S. Pat. No. 6,251,061 to Hastings et al. describes a cardiac assist device using field controlled fluid. U.S. Pat. No. 6,508,756 to Kung et al. describes yet another cardiac assist device that may be active or passive.
Prior art cardiac assist systems described hereinabove suffer from a common drawback in that the diseased heart is subjected to a sudden external contracting force. This is somewhat unnatural and may be a contributory factor to the low life-expectancy of recipients using such systems.
Prior art for leg massaging includes U.S. Pat. No. 5,672,148 to Maunier, which describes a hydraulic device for lymphatic drainage and massage of the human body that comprises a chamber with outer quasi-rigid & inner supple walls, filled with porous material through which a viscous fluid is circulated. The device provides hydrostatic pressure around the limb and does not provide different pressures to different areas.
U.S. Pat. No. 5,437,610 to Cariapa et al. describes an extremity pump apparatus for the treatment of edema. A plurality of bladders arranged in a bandage for wrapping around a limb is described. The closing arrangement allows the bandage to be fitted to limbs of different sizes. The plurality of bladders is connected via a manifold and valves to a hydraulic pressure source. The prosthetic is either cylindrical or frustoconical.
U.S. Pat. No. 6,589,194 to Calderon et al. describes a device, essentially a boot, for promoting circulation by externally massaging a leg. The chambers thereof are air-filled. The pumping action is activated by movement of the wearer, particularly by wearer transferring weight from one foot to another.